It is known to provide a munitions round for a barrel-type weapon in which a propellant charge surrounds a fin-stabilized subcaliber projectile of a large length/diameter ratio which has a releasable drive cage or body separating upon the passage of the projectile and the drive body out of the barrel and permitting the projectile to travel along a ballistic or guided path thereafter.
The drive cage or body has a transition region at which it engages the projectile which form-fittingly grips the latter until the assembly of the projectile and the drive cage leave the barrel. The rear of this drive cage forms a gas-pressure-receiving surface which is usually located ahead of the center of gravity of the projectile. This surface can have a circular outer edge of a diameter substantially corresponding to the caliber of the barrel and an inner edge proximal to the outer periphery of the projectile.
A forward-facing surface of the drive cage has a forward edge which is radially spaced from the periphery of the projectile and from an inner edge substantially at the periphery of the projectile.
With projectiles or munitions rounds of the aforedescribed type it is important to increase the muzzle velocity and distance or range of the projectile which requires consideration of inner ballistics factors, barrel structure and the configuration of the projectile.
All other things being equal, the range of the projectile can be increased by minimizing the mass of the drive cage so that it forms a relatively small portion of the total mass of the munitions round and the projectile assembly.
A munitions round for the purposes described has been illustrated in U.S. Pat. No. 3,148,472 which relates to a projectile of high length/diameter ratio with a drive cage or body which is composed of a synthetic-resin material to minimize the contribution of this body to the total mass of the assembly displaced through the barrel.
Because of the significant differences in density between the drive cage and the projectile a significant difference arises in the inertias of the two members of the assembly upon firing.
To prevent axial relative movement of the drive cage and the projectile (slip) within the barrel, the two parts must be form-fittingly interconnected.
This is accomplished in the system of U.S. Pat. No. 3,148,472 by forming the drive cage or body in one piece, e.g. by injecting it or casting it around the projectile.
The material of the drive cage or body thus grips the projectile in a transition region at which high shear forces develop between projections or recesses constituting the form-fitting connection at the surface of the projectile.
To enable the significant shear forces to be withstood by the transition region a large contact area is provided between the different materials forming the connection.
However, since the drive body or cage must break away rapidly from the projectile upon the passage of the assembly from the barrel, difficulties are encountered because of the large contact area and the manner in which the form-fitting connection is made.
The aforementioned patent thus proposes to provide regions over the length of the barrel which exceed the normal caliber to create pulsation stresses in the drive cage to facilitate the rupture and separation thereof.
These expedients have been found to be disadvantageous from the point of view of the final ballistics conditions of the projectile and create other problems as well. For example, when the barrel must be modified to ensure the pulsation stresses mentioned previously, the barrel is subjected to a high degree of wear. Such wear of the barrel causes failure and misfiring or unreliable firing of the projectile. The range cannot be reliably ascertained, for example, and ultimately the final ballistics conditions are detrimentally affected.
It also may be mentioned that the increase in the range and improvement of the final ballistics conditions of the projectile by increasing the size of the charge cannot be effective with the system of U.S. Pat. No. 3,148,472 at least in part because it is necessary to increase the length of the munitions round or increase its diameter. This, of course, requires further modifications of the weapon. An increased charge, moreover, induces additional wear of the inordinately expensive weapon with the disadvantages mentioned previously.